[ivwarrior]

I'd skip the potassium permanganate idea. As stated above, it's nasty stuff if you're not careful with it. We use it at work as a regenerate in iron filters for people with high levels of iron in their well water. In addition to staining pretty much everything it touches purple, it'll also give you a few days worth of brown skin if you get it on yourself. I would imagine it'd stain the plants for a while, too.

If you really want to try it, check with your local hardware store, or if you have one nearby, a place that deals in water treatment equipment like water softeners, etc.